Have is used to make present perfect and past perfect tenses. See Have for more on have.

Stephenhas finished fixing the car.

George and Alicehave seen the show already.

Amanda had alreadyeaten when we arrived.

Theyhad notexpected to see us there.

Do is the supporting auxiliary. It is used in forming negatives, questions, and emphatic statements. See Do for more on do. See Aspect and Compound tenses for more on simple and compound verb forms.

Ido not like sausages at all.

Do youlike prawns?

Youdo like prawns, don’t you?

Will, may, might, and the other verbs listed on Modal verbs are the modal auxiliary verbs, usually called simply, modal verbs. A modal verb allows us to talk about actions as possible, doubtful, or necessary.

Charliewill go home on Friday.

Charliemay gohome on Friday.

Charliecould go home on Friday.

Charliemust go home on Friday.

Auxiliaries can be combined together in a single verb phrase. For example, a verb phrase may consist of a modal + a form of have + a form of be + a form of a main verb.

Icould have been making a bad mistake by trusting him.

Sarawill have been living in New Zealand for 2 years next month.

Youmust have been given the wrong number.

The auxiliary verb, or if there is more than one of them, the first auxiliary verb, performs these following grammatical functions:

It shows tense and is the finite part of the verb phrase.

Ihave seen it.

Shehad seen it.

Shehas been thinking.

Shehad been thinking.

It shows number and person agreement with the subject.

She has seen it.

They have seen it.

I amlooking for it.

You are looking for it.

It will take any negative immediately after it.

Ido not want to do that.

Shehas not been concentrating.

It can come before the subject to make a question.

Do you want to help us?

Have you got a mobile phone?

Contracted forms

Auxiliaries are very often used in contracted forms. In the case of be and have, the contracted form can involve linking the subject and the auxiliary verb into a single form e.g. I’m, I’ve, we’d, Sue’s (Sue has or Sue is).

We’reback!

(We areback!)

I’ve found it.

(I havefound it.)

They’d gone when I got there.

(They hadgone when I got there.)

Tom’s here.

(Tom is here.)

The contracted negative form auxiliary + n’t is common with all the auxiliaries except am, e.g. hasn’t, wouldn’t, don’t.

She isn’t (is not) trying.

Wedon’t (do not) live here.

Hehasn’t(has not) seen it.

Ican’t (cannot) come.

In standard British English, the contracted form of am not, when it is part of a question, is aren’t I.

Aren’t I going to need some matches?

I’m getting a lift with you,aren’t I?

Contracted forms are more informal than full forms. They are therefore more common in spoken English. Full forms are usually preferred in formal written English.

Auxiliaries are used in sentence tags. See Sentence tags for more about sentence tags.

You had only just bought that carpet when the kitchen flooded,hadn’t you?

It’s Katie’s birthday on Saturday,isn’t it?

You are joking,aren’t you?

Auxiliaries are also used to make a short addition to a statement, such as:

a positive addition to a positive statement, accompanied by so or too.

I went to the park and Lucy did too.

I loved the film, andso didFinlay.

a negative addition to a negative statement, accompanied by neither or nor.

My dad never eats mussels andneither do I.

I don’t want to speak to William now. –Nor doI.

I can’t understand it. –Neither can I.

Auxiliaries can be used in positive sentences to give emphasis. When they are emphatic they are never contracted.

Youhavemade a mess!

Thatwas a nice surprise!

Iam proud of Katie. She’s so clever.

In the present simple tense and the past simple tenses the appropriate form of do is used to show emphasis.

Ido like Penny. – So do I.

Wedid have a lovely time.

An auxiliary on its own can be used to give a short answer to a question. Whatever auxiliary is used in the question is used on its own in the answer. The main verb is not repeated. Short answers are very common in spoken English.